A method for reducing and blocking leachate sources in tailings ponds

Abstract

This invention relates to the field of tailings dam pollution prevention and control, and discloses a method for reducing leachate sources and blocking leakage in tailings dams. The method includes at least the steps of identifying leakage problems and constructing a blocking system. Leakage problem identification includes the following steps: S1: basic data collection and on-site investigation; S2: acquisition of leachate leakage and diffusion channels through multi-source data fusion. The blocking system construction includes the following steps: S3: determining whether the tailings dam is operational; if so, proceed to S4; otherwise, proceed to S6; S4: analysis of pollutant release mechanisms and pollution characteristics in the tailings dam; S5: design and implementation of pollutant source reduction schemes; S6: design and construction of tailings dam leakage blocking structures. This invention constructs a complete tailings ecological environment governance system from leakage, pollution identification, source blocking to ecological restoration, and adopts a comprehensive prevention and control method covering source reduction and diffusion paths of tailings pollution release to block the spread of pollution sources.

Description

Technical Field

[0001] This invention relates to the field of tailings dam pollution prevention and control, and in particular to a method for reducing and blocking the source of leachate from tailings dams. Background Technology

[0002] With the rapid development of my country's economy and society, the demand for mineral resources is increasing daily, but this has also led to a massive accumulation of tailings. Currently, my country has over 12,000 tailings ponds, with a total stockpile of 15 billion tons. As the largest solid waste source in my country in terms of both quantity and output, tailings not only occupy vast amounts of soil resources during storage but also easily cause environmental pollution. Metal tailings contain various heavy metals and non-metallic elements such as sulfur and arsenic, which are easily leached by rainwater or surface water. Due to their small particle size and large specific surface area, tailings readily release large amounts of heavy metal ions under the influence of water. Furthermore, tailings deposits are primarily composed of sand particles, and their excellent permeability facilitates the diffusion of pollutants. Currently, tailings ponds can be categorized based on their location within the terrain into valley-type, river valley-type, hillside-type, flatland-type, and sewer-type tailings ponds. Under normal circumstances, surface water and atmospheric precipitation seep into the soil and groundwater below the tailings dam through vertical infiltration or lateral runoff, and then spread outward with the groundwater flow, further polluting the groundwater and soil outside the tailings dam.

[0003] Currently, the main methods for preventing heavy metal pollution from tailings dam leachate include physical shielding, extraction treatment, and original remediation. Physical shielding primarily uses concrete, cement, geotextiles, etc., to construct physical barriers to prevent pollutant diffusion. This method is generally used in newly constructed tailings dams but is less suitable for existing operational tailings dams. Extraction treatment involves extracting contaminated groundwater or leachate and treating it using physical, chemical, and biological techniques. This method can reduce the spread of heavy metal-containing wastewater to the surrounding area; however, it requires a well system and long-term operation, resulting in high maintenance and treatment costs, making it unsuitable for large-scale groundwater pollution. Permeable reactive barriers, as an in-situ treatment technology, involve placing permeable reactive grids downstream of the contaminated water to remove pollutants through chemical, physical, and biological methods. However, this method is less suitable for complex geological environments such as fissure seepage and dissolution channel seepage.

[0004] In addition, at present, tailings leachate is usually treated by setting up wastewater collection ponds and treatment plants at the end of the process. However, this treatment method has the problem of mixing sewage, groundwater and rainwater, large sewage treatment volume, limited treatment capacity during the flood season when the water volume is large, and the treatment plant requires long-term operation and maintenance, and the sludge produced presents a problem of secondary treatment.

[0005] Therefore, the existing technology has the following technical problems:

[0006] 1. Physical shielding is not a suitable solution for preventing seepage in operating tailings dams;

[0007] 2. The waste of resources, high long-term operation and maintenance costs, and secondary waste disposal problems caused by the use of pumping treatment and the construction of downstream sewage treatment plants;

[0008] 3. In-situ treated anti-seepage reactive walls are difficult to adapt to complex geological environments and difficult to control the total amount of pollutants at the source.

[0009] 4. No systematic pollution prevention methods have been developed from the source to the process.

[0010] Meanwhile, how to reduce the leaching of pollutants in tailings and prevent the leakage of leachate, so as to achieve in-situ blocking of pollutant leakage and diffusion in tailings ponds, is a key technical issue in controlling tailings pond pollution. Summary of the Invention

[0011] To overcome the above technical problems, the purpose of this invention is to provide a method for reducing the source of tailings dam leachate and blocking leakage. This method reduces pollutants at the source by inhibiting the leaching and diffusion of heavy metals from tailings dams, while simultaneously blocking and isolating leachate leakage channels to block both the source and diffusion channels of pollutants. The combination of these two methods effectively blocks the diffusion of pollutants from tailings dams, achieving a long-term, efficient, and low-cost solution to the problem of groundwater and soil pollution caused by tailings dam leachate leakage.

[0012] Source reduction includes mixing antioxidant materials at the tailings discharge outlet, setting up adsorption wells before the seepage outlet, and setting up runoff interception and drainage ditches around the tailings. A method and system for source reduction and leakage blocking of tailings dam leachate includes three blocking structures: seepage barrier wall adsorption blocking, seepage channel sealing blocking, and end-of-pipe treatment adsorption blocking.

[0013] This invention provides the following technical solution:

[0014] A method for reducing and blocking leachate sources in tailings ponds includes at least the steps of identifying leakage problems and constructing a blocking system, wherein the identification of leakage problems includes steps S1 and S2:

[0015] S1: Basic data collection and on-site reconnaissance. Collect geological and basic data of the tailings dam and conduct on-site reconnaissance; preliminarily ascertain the boundary conditions, filling conditions, distribution and collection characteristics of surrounding surface water, surface leakage and pollution characteristics of the tailings dam; collect and analyze the operation status of the tailings dam; proceed to S2.

[0016] S2: Acquisition of leachate leakage and diffusion channels through multi-source data fusion, identification of major pollution diffusion channels, acquisition of surface water and groundwater recharge, flow, and discharge within the site, as well as leakage methods, locations, and flow rates;

[0017] The construction of the blocking system includes the following steps:

[0018] S3: Determine if the tailings dam is running. If yes, proceed to S4; otherwise, proceed to S6.

[0019] S4: Analysis of pollutant release mechanism and pollution characteristics in tailings ponds. Through tailings infiltration tests, the leaching characteristics and types of pollutants are analyzed. Through tailings leachate diffusion characteristic tests, hydrogeological surveys and soil analysis of the site are conducted to analyze the diffusion characteristics of tailings leachate and the pollution characteristics of the site. Proceed to S5.

[0020] S5: Design and implementation of pollutant source reduction schemes, selection of mixed antioxidant materials and proportions; design of seepage adsorption well pore location, depth, well structure and adsorption materials; design of the length, slope, cross-section and energy dissipation sedimentation tank structure of the surface runoff interception and drainage ditch around the tailings dam, proceed to S6;

[0021] S6: Design and construction of tailings dam leakage blocking structures: Based on the leakage situation of the overburden and rock fissures, the distribution of leakage channels, and the downstream leakage situation, select one or more blocking structures for design and construction.

[0022] According to some implementation methods, the multi-source data fusion in step S3 involves selecting and fusing geological information obtained by any single or combined methods of geophysical exploration, drilling, and geochemical exploration, constructing a three-dimensional geological model of leakage and diffusion, and comprehensively analyzing and inverting the three-dimensional geological model to obtain the location of leakage channels and seepage paths.

[0023] In the above implementation, the acquisition of leachate leakage and diffusion channels by multi-source data fusion is to integrate the results obtained by geophysical exploration, drilling and geochemical exploration to construct a three-dimensional geological model of leakage and diffusion. Previous technologies only used and analyzed a single method and did not have a method and model for multi-source data fusion.

[0024] According to some implementation methods, the tailings leachate test in step S4 restores the environment of the tailings sample through one-dimensional consolidation and leaching through a dynamic and continuous process, thus restoring the pollutant release environment of the original tailings accumulation state; the tailings leachate diffusion characteristic test simulates the pollutant migration process under multiple geological conditions, different depths, and osmotic pressures using a two-dimensional diffusion and migration test device.

[0025] According to some implementation methods, the tailings percolation test in step S4 includes the following steps:

[0026] S4-11: Using a consolidation-controlled one-dimensional seepage leaching test device, core samples from the tailings dam were cut and taken every 1.0 m with a ring cutter;

[0027] S4-12: Place the sample into a permeation leaching test apparatus until saturated. After saturation, conduct continuous permeation tests to analyze the changes in pollutant composition and content in the leachate after 1h, 5h, 12h, 24h, 3d, 5d, 7d, 14d, and 28d of permeation, and analyze the continuous leaching mechanism of pollutants.

[0028] According to some implementation methods, the tailings leachate diffusion characteristic test in step S4 includes the following steps:

[0029] S4-21: Reconstruct a geological model within a two-dimensional pollutant diffusion sandbox based on the stratigraphic structure obtained from the exploration;

[0030] S4-22: Based on the leachate analysis results, prepare a diffusion solution, place the diffusion solution in a simulated diffusion sand box, apply an osmotic pressure of 20-200 kPa, extract and analyze the concentration of pollutants in water and soil at different distances and depths after diffusion for 1 h, 5 h, 12 h, 24 h, 3 d, 5 d, 7 d, 14 d, and 28 d, and analyze the diffusion characteristics.

[0031] According to some implementations, step S6 is followed by the following steps:

[0032] S7: Ecological restoration of non-filling areas of tailings ponds: constructing a vegetation layer using tailings sand and glutinous rice paste ecological restoration materials and slow-release fertilizer, and selecting native species to restore vegetation diversity;

[0033] According to some implementations, step S6 is followed by the following steps:

[0034] S8: Evaluation of source reduction and blocking effect: Groundwater monitoring wells are set up outside the seepage prevention curtain at the downstream seepage diffusion channel and the lateral runoff channel of the tailings dam to monitor changes in groundwater level and heavy metal content in groundwater, thereby evaluating the source blocking effect.

[0035] According to some implementations, in step S6, the method for constructing the single or multiple blocking structures is selected from the following single or multiple construction methods:

[0036] The construction method of the first blocking structure is to design the seepage barrier wall, construct the mud drainage channel, and construct the seepage barrier wall in sequence according to the leakage of the overburden and rock fissures.

[0037] The construction method of the second blocking structure is to sequentially carry out the design of seepage channel sealing grouting, grouting hole and seepage prevention grouting construction according to the distribution of seepage channels.

[0038] The third method for constructing the blocking structure involves designing and constructing the adsorption structure at the end of the downstream collection tank according to the downstream leakage situation.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention provides a method for reducing the source of leachate from tailings ponds and blocking leakage, which can be used for the treatment of underground leakage of pollutants from tailings dams and landfills.

[0041] It has constructed a complete set of tailings ecological environment governance methods, from leakage, pollution identification, source blocking to ecological restoration. It adopts a comprehensive prevention and control method that covers the source reduction of tailings pollution release and the source blocking of diffusion paths. While blocking the pollution source, it has carried out ecological restoration of tailings ponds and restoration of vegetation communities.

[0042] This invention's source reduction method can reduce pollutant emissions at the source and achieve rapid replacement of adsorbent materials, solving the problem of the difficulty in replacing traditional permeable reactive walls. It addresses leakage problems in the overburden and deep bedrock fissures without affecting the normal operation of tailings ponds or landfills, and solves the problem of uneven grout diffusion and discontinuous seepage prevention structures in conventional grouting methods. It also solves the problems of high grout consumption and poor seepage prevention effect caused by the erosion and dispersion of conventional cement grout under groundwater conditions, and the resulting loose curtain structure. Simultaneously, it utilizes the properties of the grout to filter the leachate, ensuring that the leachate meets water discharge standards. This source reduction and blocking method avoids the long-term transportation and maintenance required for upstream extraction and downstream collection methods, solves the problems of resource waste and secondary waste treatment in existing technologies, reduces long-term operating costs, and significantly reduces the leakage risk from downstream collection or in-situ downstream treatment, forming a systematic blocking method from the source to the process. Attached Figure Description

[0043] Figure 1 This is a flowchart of an embodiment of the tailings dam leachate source reduction and leakage blocking method provided by the present invention;

[0044] Figure 2 This is a schematic diagram of lateral seepage sealing of pollutants in a tailings dam provided in Embodiment 1 of the present invention;

[0045] Figure 3 This is a schematic diagram of the overall cross-section of the tailings dam for reducing pollutant sources and blocking leakage, provided in Embodiment 2 of the present invention.

[0046] Figure 4 This is a schematic diagram of the hollow permeation adsorption rod structure provided in Embodiment 3 of the present invention;

[0047] Figure 5This is a schematic diagram of the pump suction adsorption plate structure provided in Embodiment 3 of the present invention.

[0048] The attached image is labeled as follows:

[0049] 1. Flexible seepage barrier wall; 2. Blocking body; 3. Liquid collection tank adsorption system; 4. Adsorption well; 5. Mineral sand discharge outlet; 6. Interception and drainage system; 7. Reconstructed vegetation layer; 401. Fine-porous attapulgite soil structure; 402. Ultra-fine-porous attapulgite soil structure; 403. Permeable reaction membrane; 404. Membrane support; 405. Hollow lifting pipe; 301. Pump suction adsorption plate shell; 302. Fine-porous attapulgite soil plate; 303. Permeable reaction membrane; 304. Membrane support plate; 305. Pump suction pipe. Detailed Implementation

[0050] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0051] like Figure 1 This invention provides a method for reducing the source of tailings dam leachate and blocking leakage. The principle is to reduce the source of pollutants by inhibiting the leaching and diffusion of heavy metals in the tailings dam, and at the same time, to block and isolate the leakage channels of leachate to block the diffusion channels of pollutants. The combination of the two methods can block the source of pollutant diffusion in tailings dams, and achieve a long-term, efficient and low-cost solution to the problem of groundwater and soil pollution caused by tailings dam leachate leakage.

[0052] The invention will now be further described with reference to the accompanying drawings.

[0053] Example 1

[0054] In this embodiment, taking the prevention and control of leachate pollution from a closed tailings dam as an example, the tailings dam is covered with clay, and a drainage ditch is set within the tailings dam cover layer. The tailings dam is a vertical concrete gravity retaining wall, and a collection pool is set downstream of the tailings dam. It is laterally recharged by groundwater and leaks laterally through fissures in the bedrock below the dam. The basic steps of this method for reducing the source of leachate from the tailings dam and blocking leakage are as follows:

[0055] First, identifying pollution problems;

[0056] Second, the construction of a system for blocking and ecological restoration;

[0057] Third, effect evaluation.

[0058] More specifically, the first step in identifying pollution problems is as follows:

[0059] Step 1: Basic Data Collection and Site Survey

[0060] (1) Collect the design and construction data of the closed tailings ponds, and obtain the tailings filling depth h, the thickness of the overlying soil layer d, and the tailings pond structure.

[0061] (2) On-site survey: Determine the boundaries between the existing tailings fill and the closed reservoir, as well as the surface water runoff.

[0062] Step 2: Investigation and Acquisition of Leachate Leakage Channels through Multi-Source Data Fusion

[0063] (1) Comprehensive geophysical exploration to obtain seepage channels: The location of the seepage inlet of the tailings dam was determined by using pseudo-random current field generation. The points were scattered within 10-15m in front of the dam in the tailings dam, with a spacing of 1-2m. The natural electric field method was used to set up measuring points on the top of the tailings dam, the downstream slope of the dam and the left and right banks, with a spacing of 2-4m. The high-density electrical resistivity method was used to set up measuring points on the top of the dam, the downstream slope of the dam and the left and right banks, with a spacing of 1-2m.

[0064] (2) Exploration borehole layout: Based on the comprehensive geophysical survey, boreholes are arranged from upstream to downstream at locations where leakage channels may exist. The borehole spacing and row spacing are 3 to 5 m. Temperature field and flow field tests are conducted inside the boreholes.

[0065] (3) Perform multi-source data comprehensive analysis and inversion on geophysical and drilling data to obtain the location of seepage channels and seepage paths.

[0066] Second, the specific steps for the components of the leakage prevention and ecological restoration system are as follows:

[0067] Step 3: Design of the blocking scheme

[0068] Based on the development characteristics of the seepage channels and the location of the impermeable layer, the sealing layer and sealing method are determined, and the seepage channel blocking method among the three blocking methods is selected. For tailings dam seepage blocking, priority should be given to sealing the seepage inlet at the lower part of the dam foundation and the seepage channels at the lower part of the dam foundation; for seepage along the lateral runoff zone of the tailings dam, an impermeable layer can be constructed between the seepage zone and the impermeable layer to block the seepage.

[0069] Step 4: Construction of the seepage prevention layer at the tailings dam's seepage source and lateral runoff blocking layer

[0070] (1) Arrangement of seepage prevention boreholes: Arrange 2-3 rows of seepage prevention grouting holes in a quincunx pattern along the upstream front edge of the dam body. The initial hole spacing is set at 2m. Adjust the hole spacing through pilot hole grouting test and select 1.7 times the diffusion radius as the hole spacing. When there is no seepage prevention curtain at the front edge, a row of seepage prevention grouting holes can be set at the initial dam crest centerline position and 2 more rows of seepage prevention grouting holes should be constructed downstream of the dam foundation.

[0071] (2) See Figure 2 A second blocking structure was installed inside the tailings dam. This second blocking structure is a blocking body 2, which is a grouting block for sealing deep seepage channels. The grouting is divided into two parts: blocking groundwater recharge channels and blocking lateral seepage channels of leachate. Drainage interception systems 6 were installed on the slope of the tailings dam to intercept surface runoff from replenishing the tailings dam water. Source reduction is achieved through the blocking body 2 and drainage interception systems 6. Specifically, the arrangement of boreholes for blocking lateral runoff inside the dam is as follows: based on the identification characteristics of seepage channels, 1-2 rows of grouting holes are arranged in a triangular structure at the lateral runoff seepage locations inside the tailings dam, and 1-2 rows of grouting holes are arranged at the lateral runoff seepage locations. The initial hole spacing is set at 2m. The hole spacing is adjusted through pilot hole grouting tests, and a spacing of 1.7 times the diffusion radius is selected.

[0072] (3) Drilling structure: The hole is formed by using an impact rotary drilling rig with an opening diameter of 110mm. After passing through the dam foundation, a 110mm casing is installed and a 90mm drill bit is used to drill into the water-resistant layer for 1.0m.

[0073] (4) Grouting method: pure pressure grouting with membrane bags is adopted, and the grouting pressure is 1.0 to 2.0 MPa;

[0074] (5) Grouting material: The grout is composed of cement, water and viscosity-varying composite admixture, with a water-cement ratio of 0.6 to 1.0. The addition amounts of admixtures 1#, 2# and 3# are 0.33%, 1.8 to 2.4%, and 0.5 to 1.0%, respectively. The pumpable period of the grout is 20 to 40 minutes, the initial setting time is 180 to 360 minutes, and the water absorption rate is <0.5%.

[0075] Step 5: Ecological restoration of tailings dam fill layer

[0076] (1) Reconstruction of the vegetation layer in the fill layer: In the yellow clay layer, the soil structure is reconstructed by deep plowing and mixing, with humus black soil and 1% to 2% of the total soil volume of slow-release fertilizer mixed into the soil layer at a ratio of 0.1 to 0.5:1.

[0077] (2) Vegetation restoration: select pioneer plants such as Artemisia annua for seed sowing.

[0078] Third, the specific steps for evaluating the effect are as follows:

[0079] Step 6: Groundwater Monitoring

[0080] Groundwater monitoring wells are installed outside the seepage prevention curtain at the downstream seepage diffusion channel and the lateral runoff channel of the tailings dam to monitor changes in groundwater level and heavy metal content in groundwater, thereby assessing the effectiveness of source blocking.

[0081] Example 2

[0082] In this embodiment, the source of leachate from a tailings dam in an operating lead-zinc mine is reduced and blocked. The tailings dam is constructed using an upstream tailings dam method. The initial tailings dam is a primary masonry gravity dam, and the secondary dam is a 6-stage tailings accumulation body. The main leakage is from fissures in the foundation rock mass. The specific steps for blocking the leakage are as follows:

[0083] First, identifying pollution problems;

[0084] Second, source reduction and blocking, and the construction of an ecological restoration system;

[0085] Third, effect evaluation.

[0086] More specifically, the first step in identifying pollution problems is as follows:

[0087] Step 1: Basic Data Collection and Site Survey

[0088] (1) Collect the structural parameters of the initial dam body and sub-dam body, including the height H of the dam body, the width of the dam crest D1 and the width of the dam bottom D2;

[0089] (2) On-site survey: Ascertain the boundaries of the existing tailings dam and the surface water runoff.

[0090] Step 2: Investigation and Acquisition of Leachate Leakage Channels through Multi-Source Data Fusion

[0091] (1) Comprehensive geophysical exploration to obtain seepage channels: The location of the seepage inlet of the tailings dam was determined by using pseudo-random current field on the initial dam and the first two sub-dams. The points were arranged in a scattered manner with a spacing of 1 to 2 m. The natural electric field method was used to arrange measuring points on the top of the initial dam, the downstream slope, the left and right banks, and the downstream of the tailings dam with a spacing of 2 to 4 m. The high-density electrical resistivity method was used to arrange measuring points on the top of the dam, the downstream slope, the left and right banks, and the downstream of the tailings dam to arrange the measuring slope with a spacing of 1 to 2 m.

[0092] (2) Exploration borehole layout: Based on the comprehensive geophysical survey, boreholes are arranged downstream along the first two sub-dams at locations where leakage channels may exist. The borehole spacing and row spacing are 3-5m. Temperature field and flow field tests are conducted inside the boreholes.

[0093] (3) Construct a multi-source data model from geophysical and drilling data, perform comprehensive analysis and inversion on the multi-source data model, and obtain the location of leakage channels and seepage paths.

[0094] Step 3: Analysis of pollutant release mechanism and pollution characteristics in tailings ponds

[0095] Heavy metal analysis was conducted using groundwater monitoring wells distributed across tailings dams at various levels to determine the content of pollutants in the groundwater and to clarify the groundwater flow rate and infiltration line height.

[0096] In-situ tailings samples were obtained by drilling (every 1.5m to 2m). A one-dimensional seepage leaching test device with consolidation control was used. After saturation, continuous seepage tests were conducted to analyze the changes in pollutant composition and content in the leachate after 1h, 5h, 12h, 24h, 3d, 5d, 7d, 14d, and 28d of seepage, and to analyze the continuous leaching mechanism and leaching amount of pollutants.

[0097] Second, source reduction and seepage prevention, and the construction of an ecological restoration system, the specific steps are as follows;

[0098] Step 4: Determine the source reduction and leakage prevention plan

[0099] Based on the characteristics of atmospheric precipitation and surface runoff, intercepting drainage ditches are arranged to reduce water volume; the sealing layer and sealing method are determined according to the development characteristics of seepage channels and the location of the aquitard; the pollutant source adsorption structure and adsorption materials are designed according to the content of groundwater pollutants and groundwater flow. Taking lead-zinc mine as an example, its characteristic pollutants mainly include Pb, Zn, Cd and Cu, and the selected adsorption material is modified clay adsorption material.

[0100] Step 5: Construction of intercepting and drainage ditches to reduce water volume at the source

[0101] As attached Figure 3 The central interception and drainage system 6, specifically the interception and drainage ditch, is located above the designed sealing elevation of the tailings dam and covers the entire dam area, including drainage ditches and energy dissipation sedimentation ponds.

[0102] Step 6: Construction of seepage prevention wall at the source of tailings dam seepage.

[0103] (1) Anti-seepage structure design: Based on the seepage situation of the overburden and rock fissures, a flexible anti-seepage wall and anti-seepage curtain grouting holes are arranged downstream of the dam body. The curtain holes are divided into upper, middle and lower rows of holes according to the seepage direction.

[0104] (2) Curtain grouting construction: According to the design, boreholes are laid out downstream of the dam or around the landfill. The boreholes sequentially penetrate the overburden layer, soft soil layers such as sand and gravel layers, weathered bedrock, and fractured bedrock, until they penetrate 0.5 to 1.0 m below the intact bedrock. Then, time-varying viscosity grout is used for closed-loop grouting in the boreholes. The grouting borehole construction follows the sequence of upper row, lower row, and middle row of holes, as shown in the attached diagram. Figure 3 A schematic diagram of the middle blocking body 2.

[0105] (3) Construction of mud drainage channels: The drainage channels with a height of 20-30cm and a width of 60-1.0m are constructed by masonry and distributed on both sides of the grouting hole axis.

[0106] (4) Construction of a seamless flexible cutoff wall: Under the axis of the curtain grouting holes, a vibratory compaction caisson is used for trenching construction of the cutoff wall. The caisson is selected according to the designed thickness and depth of the cutoff wall, and should penetrate the overburden layer to the top of the grouting layer. Then, the cutoff wall grout is injected, and the vibratory compaction caisson is lifted, as shown in the attached... Figure 3 Medium-flexible seepage barrier wall 1.

[0107] (5) Select time-varying viscosity grout as the grouting material for the upper, middle and lower grouting holes. The water-cement ratio of the grout is 0.6 to 0.8. The addition ratio of patented time-varying viscosity grouting materials 1#, 2# and 3# is 0.3 to 0.5%, 1.2 to 2.2% and 0.8 to 1.5%, respectively. The fluidity and pumpability of the grout are determined according to the degree of crack development. Under normal circumstances, the pumpability of the grout is selected as 15 to 25 minutes.

[0108] Step 7: Construction of pollutant source adsorption structure in tailings dam

[0109] (1) On the top sub-dam, use an impact rotary drilling rig to drill and construct adsorption well 4 with a hole diameter of 200m and a drilling depth ≥3m into the saturation line. The hole spacing is 3m. At intervals of one sub-dam, set up secondary adsorption wells with the same parameters at staggered positions on the sub-dam. The number of adsorption wells 4 is up to the initial dam. The casing is a perforated pipe structure. The length of the perforated pipe should be 2-3m higher than the current saturation line. Weld wire mesh with a hole diameter of less than 1mm inside the perforated pipe.

[0110] (2) Depending on the type of pollutant, attapulgite is placed in the adsorption well, and the length of the attapulgite is the same as the length of the flower tube.

[0111] Step 8: Ecological restoration of the tailings dam surface

[0112] In the non-landfill area, a 10cm thick waterproof layer is constructed by mixing patented glutinous rice paste with tailings sand. Then, a 20cm thick vegetation layer is built using a mixture of patented dual-polymer material, slow-release fertilizer, grass seeds, and tailings sand. Interception ditches are installed at the tailings boundary to prevent runoff from accumulating on the slope, forming... Figure 3 7. Reconstruct the vegetation layer in the middle.

[0113] Third, effect evaluation, the specific steps are as follows:

[0114] Step 9: Groundwater Monitoring

[0115] Groundwater monitoring wells are installed outside the seepage prevention curtain at the downstream seepage diffusion channel and the lateral runoff channel of the tailings dam to monitor changes in groundwater level and heavy metal content in groundwater, thereby assessing the effectiveness of source blocking.

[0116] Example 3

[0117] In this embodiment, the source of leachate from an operating tailings dam is blocked. The tailings dam is an upstream tailings dam, consisting of a masonry gravity dam and a tailings accumulation body. The leachate mainly seeps downstream through bedrock fissures and fill layers below the tailings dam, and a collection pond is located downstream of the tailings dam. The blocking steps include:

[0118] Step 1: Basic Data Collection and Site Survey

[0119] Tailings Dam Geological Data: Collect basic engineering geological and hydrogeological data and maps of tailings dams and their adjacent areas;

[0120] Basic data for tailings dams: collect design and construction reports and drawings, and operation records of tailings dams; for dams that have been closed, collect the closure design and acceptance reports and drawings.

[0121] On-site investigation: Preliminary investigation revealed the boundary conditions of the tailings dam, the filling conditions, the distribution and collection characteristics of surrounding surface water, and the characteristics of surface seepage and pollution.

[0122] Step 2: Investigation and Acquisition of Leachate Leakage and Diffusion Channels through Multi-Source Data Fusion

[0123] By employing drilling, geophysical exploration, and geochemical methods, and utilizing multi-source data coupling techniques, we determined the seepage channels of tailings leachate, identified the main pathways for pollution diffusion, and clarified the recharge, flow, and discharge of surface water and groundwater within the site, as well as the seepage patterns, locations, and flow rates.

[0124] As a specific implementation plan, the method for obtaining the leakage channels and strata is as follows:

[0125] (1) Comprehensive geophysical exploration to obtain the seepage area: The location of the seepage inlet of the tailings dam is determined by using pseudo-random current field generation. The points are arranged in a scattered manner within 10-15m in front of the dam in the tailings dam, with a point spacing of 1-2m. The natural electric field method is used to arrange measuring points on the top of the tailings dam, the downstream slope of the dam and the left and right banks, with a measuring point spacing of 2-4m. The high-density electrical resistivity method is used to arrange measuring points on the top of the dam, the downstream slope of the dam and the left and right banks to set up the measurement slope, with a measuring point spacing of 1-2m.

[0126] (2) Geological drilling to obtain and locate seepage: Based on the existing geophysical exploration results, exploration boreholes are laid out in the seepage areas upstream and downstream of the tailings dam using engineering geological exploration and hydrogeological exploration drilling methods. The borehole range covers the seepage area of ​​the dam body. The positions of the boreholes at both ends should extend 2m beyond the boundary line of the two ends of the seepage, and the internal borehole spacing should be 3-5m. The exploration borehole depth should penetrate 0.5-1.0m into the intact bedrock. Using the exploration boreholes, combined with the method of geophysical exploration in the boreholes, the seepage characteristics between the boreholes and deep in the bedrock are identified.

[0127] (3) Take rock core samples at intervals of 0.5 to 1.0 m in the borehole. After the groundwater is exposed, take water samples for analysis. Use the source reduction borehole in the tailings dam and the borehole at the front edge of the tailings dam for tracer tests to determine the seepage layer and seepage path.

[0128] (4) Using multi-source data from integrated geophysical exploration, drilling and geochemistry, construct a three-dimensional structure of the seepage zone and diffusion zone.

[0129] Multi-source data fusion is the process of integrating and eliminating errors using mathematical models. The multi-source data comes from geological information obtained by any single or combined methods of geophysical exploration, drilling, and geochemical exploration. Based on the data from geophysical exploration, a three-dimensional geological model composed of cross-sectional and longitudinal planes is constructed. The stratigraphic structure and lithology obtained from drilling are added to the basic three-dimensional geological model to establish a three-dimensional geological model that includes seepage paths.

[0130] Step 3: Analysis of pollutant release mechanism and pollution characteristics in tailings ponds

[0131] Through tailings leachate tests, the leaching characteristics and types of pollutants were analyzed; through site water level geological surveys and soil analysis, the diffusion characteristics of tailings leachate and the pollution characteristics of the site were analyzed.

[0132] Tailings leaching test method recreates the environment of tailings samples through one-dimensional consolidation and leaching, which is a dynamic and continuous process, thus restoring the pollutant release environment of the original tailings accumulation state. Diffusion characteristic test method, through a two-dimensional diffusion and migration test device, can simulate the pollutant migration process under multiple geological conditions, different depths, and seepage pressures.

[0133] As a specific implementation plan, the tailings leaching test method is as follows: using a consolidation-controlled one-dimensional seepage leaching sample device, the tailings pond core is cut and sampled every 1.0 m with a ring cutter, and placed into the seepage leaching sample device for saturation. After saturation, a continuous leaching test is carried out to analyze the changes in the composition and content of pollutants in the leachate after 1 h, 5 h, 12 h, 24 h, 3 d, 5 d, 7 d, 14 d, and 28 d of leaching, and to analyze the continuous leaching mechanism of pollutants.

[0134] As a specific implementation plan, the experimental method for the diffusion characteristics of tailings leachate is as follows: Based on the stratigraphic structure obtained from the exploration, a geological model is reconstructed in a two-dimensional pollutant diffusion sand box; based on the leachate analysis results, a diffusion liquid is prepared, and the diffusion liquid is placed in the simulated diffusion sand box. An osmotic pressure of 20-200 kPa is applied, and the concentrations of pollutants in water and soil at different distances and depths after diffusion for 1 h, 5 h, 12 h, 24 h, 3 d, 5 d, 7 d, 14 d, and 28 d are extracted and analyzed to analyze the diffusion characteristics.

[0135] Step 4: Selection and Formulation of Pollutant Source Interception Plans

[0136] The remediation plan is determined based on the tailings dam's filling structure, tailings dam structure, the development characteristics of seepage strata, and the characteristics of surface and groundwater recharge, runoff, and discharge.

[0137] The main approach is to fill the entire reservoir and address seepage at the dam foundation. The preferred methods include three types of barriers: adsorption and reduction within the fill, reduction of surface runoff, downstream construction, and surface vegetation layer construction.

[0138] As a specific technical solution, the blocking scheme includes the proportion of chemicals mixed at the tailings discharge outlet, the layout of source reduction boreholes, borehole structure, borehole depth, type and amount of adsorbent material; the scope, structure, thickness, grass species selection, and location of intercepting and drainage ditches of the runoff blocking and ecological restoration layer; the depth d, thickness h, and length L of the flexible seepage barrier wall; the layout of the curtain grouting holes, borehole depth, borehole structure, grouting pressure, grouting volume, grouting termination conditions, and other parameters, as well as the type and proportion of grout.

[0139] Step 5: Layout and Implementation of Tailings Source Reduction Plan

[0140] As a specific technical solution, tailings dam source reduction includes two parts: tailings sand leaching reduction and seepage adsorption reduction. Tailings sand leaching reduction is achieved by adding adsorbent materials to the tailings outlet and mixing them with the tailings sand to slow down the oxidation and release process of the tailings sand. Seepage adsorption reduction is achieved by setting up adsorption wells on the seepage and leaching channels of leachate to adsorb pollutant ions.

[0141] The specific implementation steps are as follows:

[0142] (1) Install a feeding mixer at the tailings outlet to form ore sand outlet 5, and add the reducing agent quantitatively into it;

[0143] (2) Select adsorption materials according to the type of tailings and the type of pollutants. Adsorption materials include attapulgite, lignin aerogel and molecular sieve materials.

[0144] (3) Source reduction adsorption borehole layout: Boreholes are arranged in a quincunx pattern for the determined tailings leaching and diffusion zone. The spacing and row spacing of the boreholes are determined based on the on-site pumping test. Half of the radius of precipitation influence is selected as the borehole spacing.

[0145] (4) Hole depth and drilling structure: A 200mm drill bit is used to open the hole and a 219mm casing is installed. If the hole collapse is encountered during the drilling process, root drilling can be used. The drilling depth should completely penetrate the tailings accumulation body and enter the lower rock and soil body by 0.5m. The lower part of the casing should use a perforated pipe with the same length as the groundwater level in the tailings. The hole spacing of the perforated pipe structure is 10-20cm. Each ring of the casing wall is set with 4 holes, and the holes of the rings are staggered.

[0146] (5) Addition of Adsorbent Material: The adsorbent material is added using a liftable feeding cylinder, and the addition depth should ensure that the adsorbent material covers at least 2 / 3 of the water depth. See Appendix Figure 4 The adsorption material is a hollow permeable adsorption rod. The outermost layer of the adsorption rod is a fine-porous attapulgite soil structure 401 with a thickness of 2cm; the middle layer is an ultra-fine-porous attapulgite soil structure 402 with a thickness of 2cm; the inner side is a permeable reaction membrane 403 with a thickness of 0.5mm-1.0mm; the innermost layer is a membrane support 404; and the top is a hollow lifting tube 405.

[0147] Step 6: Runoff Reduction and Ecological Restoration in Non-Landfill Areas

[0148] In the non-landfill area, a 10cm thick waterproof layer is constructed by mixing patented glutinous rice paste with tailings sand. Then, a 20cm thick vegetation layer is constructed by mixing patented dual-polymer material, attapulgite slow-release fertilizer, grass seeds, and tailings sand. Interception drainage ditches are set up at the tailings boundary to prevent slope runoff.

[0149] Step 7: First-level barrier structure: Construction of a seamless flexible cutoff wall at the leading edge of the dam foundation

[0150] At a position 3-5m ahead of the dam foundation, the anti-seepage wall trench is constructed using vibratory compaction interlocking caissons. The caissons are selected according to the designed thickness and depth of the anti-seepage wall. The caissons should pass through the overburden layer to the top of the grouting layer. Then, the anti-seepage wall grout is injected, and the vibratory compaction caissons are lifted.

[0151] As a specific technical solution, the seamless flexible waterproof wall is constructed continuously, one wall after another, and cannot be skipped during construction to prevent the intermediate walls from becoming unconnectable.

[0152] As a specific technical solution, the interlocking vibratory compaction caisson consists of a caisson body, caisson shoe, vibratory compactor, guide rail and jet nozzle; during the construction of the flexible anti-seepage wall, the second caisson should be lowered after the first caisson has been lowered to the predetermined depth. After the second caisson has been lowered to the predetermined depth, flexible anti-seepage grout is injected into the first caisson and the caisson is grouted and lifted. Then the subsequent caissons are constructed in sequence.

[0153] As a specific technical solution, the interlocking vibratory compaction caisson mainly sinks by vibration during construction. When encountering hard soil layers or gravel layers, the jetting device is activated to assist the caisson in sinking.

[0154] As a specific technical solution, the impermeable grout is prepared by mixing cement, clay, bentonite, and admixtures. The grout composition is as follows: cement 15-25%, bentonite 3-6%, clay 30-40%, fly ash 15-25%, attapulgite 5-10%, and existing patented viscosity-varying admixtures 1# 0.3-0.5%, 2# 1.5-2.5%, and 3#.

[0155] 0.5-1.5%, wherein the component addition amount is the percentage of each component in the total volume of the slurry, and the viscosity time-varying admixture is a percentage of the cement mass.

[0156] Step 8: Double-layer blocking structure: Grouting of deep leakage channels

[0157] Curtain grouting construction: According to the design, boreholes are laid out downstream of the dam or around the landfill. The boreholes pass through the overburden layer, soft soil layers such as sand and gravel layers, weathered bedrock, and fractured bedrock in sequence, until they penetrate 0.5 to 1.0 m below the intact bedrock. Then, time-varying viscosity grout is used for closed grouting in the boreholes. The grouting borehole construction is carried out in the order of upper row of holes, lower row of holes, and middle row of holes.

[0158] As a specific technical solution, the drilling can be carried out by rotary drilling or impact rotary drilling, the final hole diameter should not be less than 60mm, the hole spacing is 1.0m to 2.5m, and the row spacing is 1.25m to 2.75m.

[0159] As a specific technical solution, borehole sealing grouting is divided into two types: pure pressure grouting and local circulation grouting. Among them, the borehole is sealed by water pressure grout stop plugs, and the length of the grouting section can be determined from 1m to 5m according to the degree of development of formation fractures. The grout stop plugs should be located on the bedrock or hard clay layer.

[0160] As a specific technical solution, the sealed borehole section is washed, and the borehole cleaning should ensure that the drainage through the stop plug is clear.

[0161] As a specific technical solution, a three-cylinder pump is used to inject a time-varying viscosity grout in stages to seal the seepage channels of pressurized dynamic water and achieve control of the dynamic water. The time-varying viscosity grout is injected continuously until the end standard is reached. A time-varying viscosity grout with a slightly longer setting time is used for continuous injection of the lower row of grouting holes, and the injection pressure of this row of holes is higher than that of the upper row of holes. The middle row of holes is injected in stages using a three-cylinder pump with cement grout, time-varying viscosity grout, or flexible anti-seepage grout. The injection pressure is the highest in this stage, which allows the grout to fully diffuse and fill the pores of the formation.

[0162] As a specific technical solution, the viscosity-time-varying grout is a cement-based grout composed of cement, water, and a viscosity-time-varying composite admixture. It features high initial fluidity, adjustable pumpability, and controllable setting time, effectively preventing erosion by flowing water and improving sealing efficiency. The preparation method is as follows: the water-cement ratio of the grout is 0.6–1.0. Admixtures #1, #2, and #3 are fully dissolved in water. Then, admixture #1 and cement are added to the water sequentially and stirred evenly. Admixtures #2 and #3 are then added and stirred for 2–3 minutes. The pumpability of the grout is 20–40 minutes, the initial setting time is 180–360 minutes, and the water absorption rate is <0.5%.

[0163] Step 9: Construct a blocking structure for the liquid collection tank adsorption system, such as... Figure 3 Liquid collection tank adsorption system 3: Liquid collection tank pump suction adsorption plate installation

[0164] As a specific technical solution, the pump-suction adsorption plates are installed in the downstream collection tank of the tailings, with a plate spacing of 1.5–2.0 m. Figure 5 .

[0165] As a specific technical solution, the pump suction adsorption plate consists of a plate made of rough attapulgite soil wrapped by the pump suction adsorption plate shell 301, which is a fine-pore attapulgite soil plate 302 with a thickness of 5cm; the inner side is a permeation reaction membrane 303 with a thickness of 0.5mm-1.0mm; the inner side is a membrane support plate 304; the hollow cavity is connected to the pump body by the pump suction pipe 305 to form internal and external osmotic pressure.

[0166] Step 10: Evaluation of the effectiveness of source reduction and blocking

[0167] Groundwater monitoring involves installing groundwater monitoring wells at the seepage and diffusion channels downstream of the tailings dam and outside the seepage prevention curtain at the lateral runoff channels to monitor changes in groundwater level and the content of heavy metals in the groundwater, thereby assessing the effectiveness of source blocking.

[0168] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for reducing and blocking leachate sources in tailings ponds, comprising at least the steps of identifying leakage problems and constructing a blocking system, wherein the identification of leakage problems includes steps S1 and S2: S1: Basic data collection and on-site reconnaissance. Collect geological and basic data of the tailings dam and conduct on-site reconnaissance; preliminarily ascertain the boundary conditions, filling conditions, distribution and collection characteristics of surrounding surface water, surface leakage and pollution characteristics of the tailings dam; collect and analyze the operation status of the tailings dam; proceed to S2. S2: Acquisition of leachate leakage and diffusion channels through multi-source data fusion, identification of major pollution diffusion channels, acquisition of surface water and groundwater recharge, flow, and discharge within the site, as well as leakage methods, locations, and flow rates; The construction of the blocking system includes the following steps: S3: Determine if the tailings dam is running. If yes, proceed to S4; otherwise, proceed to S6. S4: Analysis of pollutant release mechanism and pollution characteristics in tailings ponds. Through tailings infiltration tests, the leaching characteristics and types of pollutants are analyzed. Through tailings leachate diffusion characteristic tests, hydrogeological surveys and soil analysis of the site are conducted to analyze the diffusion characteristics of tailings leachate and the pollution characteristics of the site. Proceed to S5. The tailings percolation test includes the following steps: S4-11: First, use a ring cutter to cut and sample the tailings dam core every 1.0m; S4-12: Then, the sample is placed in a one-dimensional permeation leaching test device to saturate the sample. After saturation, a continuous permeation test is carried out to analyze the changes in the composition and content of pollutants in the leachate after 1h, 5h, 12h, 24h, 3d, 5d, 7d, 14d, and 28d of permeation, and to analyze the continuous dissolution mechanism of pollutants. The tailings leachate diffusion characteristic test includes the following steps: S4-21: Reconstruct a geological model within a two-dimensional pollutant diffusion sandbox based on the stratigraphic structure obtained from the exploration; S4-22: Based on the leachate analysis results, prepare a diffusion solution, place the diffusion solution in a two-dimensional pollutant diffusion sand box, apply an osmotic pressure of 20~200kPa to the diffusion solution, extract and analyze the concentration of pollutants in water and soil at different distances and depths after diffusion for 1h, 5h, 12h, 24h, 3d, 5d, 7d, 14d, and 28d, and analyze the diffusion characteristics. S5: Design and implementation of tailings dam source reduction scheme, which includes tailings sand leaching reduction and seepage adsorption reduction; the tailings sand leaching reduction is achieved by adding adsorbent material to the tailings discharge outlet and mixing it with the tailings sand to slow down the oxidation release process of the tailings sand; the seepage adsorption reduction is achieved by setting up adsorption wells on the leachate seepage and leaching channels to adsorb pollutant ions and enter S6. S6: Design and construction of tailings dam leakage blocking structures: Based on the leakage situation of the overburden and rock fissures, the distribution of leakage channels and the downstream leakage situation, select one or more blocking structures for design and construction. The blocking structure is selected from any of the following structures: The first blocking structure consists of a seepage barrier wall and a mud discharge channel constructed downstream of the dam body, based on the leakage situation of the overburden and rock fissures. The second blocking structure is an anti-seepage grouting method based on the distribution of the leakage channels; The third blocking structure is an adsorption structure at the end of the downstream collection pool, which is located downstream of the tailings dam, according to the downstream leakage situation.

2. The method for reducing and blocking leachate sources in tailings ponds according to claim 1, characterized in that, The multi-source data fusion mentioned in step S2 involves selecting and fusing geological information obtained by any single or combined methods of geophysical exploration, drilling, and geochemical exploration, constructing a three-dimensional geological model of leakage and diffusion, and comprehensively analyzing and inverting the three-dimensional geological model to obtain the location of leakage channels and seepage paths.

3. The method for reducing and blocking leachate sources in tailings ponds according to claim 1, characterized in that, The tailings leachate test described in step S4 restores the environment of the tailings sample through one-dimensional consolidation and leaching through a dynamic and continuous process, thus restoring the pollutant release environment of the original tailings accumulation state; the tailings leachate diffusion characteristic test simulates the pollutant migration process under multiple geological conditions, different depths, and osmotic pressures using a two-dimensional diffusion and migration test device.

4. The method for reducing and blocking leachate sources in tailings ponds according to claim 1, characterized in that, Step S6 is followed by the following steps: S7: Ecological restoration of non-filling areas of tailings ponds: using tailings sand and glutinous rice paste as ecological restoration materials and slow-release fertilizer to construct a vegetation layer, and selecting native species to restore vegetation diversity.

5. The method for reducing and blocking leachate sources in tailings ponds according to claim 4, characterized in that, The S7 step is followed by the following steps: S8: Evaluation of source reduction and blocking effect: Groundwater monitoring wells are set up outside the seepage prevention curtain at the downstream seepage diffusion channel and the lateral runoff channel of the tailings dam to monitor changes in groundwater level and heavy metal content in groundwater, thereby evaluating the source blocking effect.

Images